In a semiconductor memory, such as a NAND EEPROM (Electrically Erasable and Programmable Read-Only Memory), a proximity effect is shown in fine wirings such as bit lines. In order to restrict such a proximity effect, an air gap may be provided between wirings adjacent to each other.
However, if an interlayer insulation film provided on the air gap is thin, due to mechanical pressure in a CMP (Chemical Mechanical Policing) process or the like, cracks occur in the interlayer insulation film, starting from the air gap. Conversely, if the interlayer insulation film is thick, contact plugs, wirings, etc. are inevitably formed deep in the interlayer insulation film in a peripheral circuit area, which causes increase in parasitic capacitance between contact plugs, wirings, etc. adjacent to each other.